An example of a conventional control method for management of mobile terminal devices in a wireless communication network is disclosed in U.S. Pat. No. 5,212,806 (Japanese Patent Application Laid-open Gazette No. Hei 4-249443), entitled "Distributed Control Methods for Management of Migrating Data Communications Network". This patent relates to a managing method for mobile communication units in a wireless communication network having a plurality of header stations (corresponding to base station devices) performing bidirectional wireless communication with at least one mobile communication unit (corresponding to a mobile terminal device). The overall method includes (1) identifying method of header station, (2) selecting method of header station, (3) registration method of mobile communication units and (4) updating and erasing method of registration contents. Essentially, the header station maintains a database called the owner table for containing identities of mobile communication units and stores a new identity whenever the header station receives a message from a mobile communication unit.
By using these methods, it is possible to not only realize cross-over movement of the mobile communication unit from a cell but also effectively utilize a battery-powered mobile communication unit.
A further example of a conventional base station selecting method there is disclosed in Japanese Patent Application Laid-open Gazette No. Hei 1-256234, entitled "Base Station Selecting Circuity". This circuit is to measure, in a mobile terminal device, a signal power received from a base station device able to communicate therewith, to obtain a number of error occurrences in the received signal, and to select the base station by using a combination of evaluation references of the received signal power and the obtained number. According to this method, it is possible to control such that a mobile terminal can select a base station device as an owner of which communicating condition with the mobile terminal device is optimum.
These conventional techniques, however, do not disclose (1) performing a re-transmission to a mobile communication unit under management of the header station, or (2) controlling the number of mobile communication units which can subscribe to the header station.
An object of the present invention is to provide a wireless LAN system capable of performing a re-transmission by a base station device and a control method thereof.
Another object of the present invention is to provide a wireless LAN system capable of limiting subscription of mobile terminal devices for a base station device and a control method thereof.
A further object of the present invention is to provide a wireless LAN system capable of correctly selecting a communicable base station device and having high communication efficiency and a control method thereof.